1. Field of the Invention
The invention relates to an oven or grill burner, i.e. a burner that can be used either for an oven or a grill, which is composed of two half shells, one whereof is perforated, which are tightly joined together along at least a portion of their edges, so as to form a tubular body communicating with a venturi tube, in which fuel gas and combustion air are mixed.
2. Description of Related Art
At present, two types of oven or grill burners exist: tubular burners and flat burners. Each of them has specific construction features, which provide a number of advantages and drawbacks, as briefly described below.
Tubular burners substantially consist of a tubular section, which has a closing member at an end, typically a plate that is shaped in such a manner as to also act as a burner fastening base. At the opposite end the tubular body is shaped, typically by a drawing process, to form a funnel-shaped, tapering section, which forms the venturi tube. A pilot burner is fitted, generally by welding, in a longitudinal lower section of the tubular body, with respect to the burner mounted condition, which pilot consists of a sheet metal half shell, at an appropriate distance from the tubular body. A parabolic reflector, which is designed to convey the flame, is fitted in a longitudinal section, which is diametrically opposite to the pilot burner attachment portion, typically by spot welding, above the tubular body.
Tubular burners have considerable construction advantages, particularly associated to the fact that they have a truncated end, which is designed to be closed by the above mentioned member. Due to this feature, burners of different lengths may be provided by cutting to length a single type of tube, or a reduced number of tube types, with no need to have in stock a plurality of parts with predetermined lengths, designed for the different uses. Furthermore, tubular burners have a particularly constant operation, regardless of the gas in use. For all these reasons tubular burners are the best suited to cover a wide market range.
Nevertheless, they also have considerable drawbacks, mainly the fact that gas outlet holes cannot have a diameter below a certain size, generally corresponding to the thickness of the wall of the tubular body, which cannot be too thin, for structural strength reasons, and for this reason the flame, and hence heat, may not be distributed in an optimized manner. Furthermore, leakage may occur from the closing member. Other problems are associated to the high cost of steel, the tubular body being generally made of this material. It shall also be considered that steel tubes are not made by extrusion but by bending a metal sheet, and so they have a longitudinal welding line, whose orientation shall be accounted for when the pilot burner and the parabolic reflector are secured. The longitudinal welding may open during the drawing process, aimed at tapering the end in which the venturi tube is provided, or said opening may occur later, during use, due to thermal shocks, with a serious damage to the manufacturer's image. Moreover, when an end of the tubular body is bent, as required if the venturi tube is to be positioned transversely, to obtain a longer tubular body (with respect to the available space inside the oven), this may cause internal stresses, which may cause the opening of the welding line. Also, fastening and sealing problems may be also generated if a member is to be fastened on the tubular body by means of screws. The ignition electrode and/or the flame safeguard are generally supported by a plate that is generally fitted between the parabolic reflector and the tubular body and whose position is very critical as the electrode and the thermocouple must be situated in a predetermined, accurate position with respect to the gas outlet holes, to prevent any ignition and/or flame detection problem. The pilot burner must be positioned in a very accurate position with respect to a row of holes formed on the tubular body, which are designed to supply gas thereto, and pilots of different lengths must be kept in stock to fit the length of the finished burner. Moreover, it has spacer feet which extend all along its length and adhere against the outer wall of the tubular wall and whose wrong positioning may cause the pilot burner holes and/or the gas outlet holes to be obstructed. Moreover, cracks may be caused by the presence of the welding, as mentioned above, by a change in the material quality and by a degraded ductility of the material in stock. For all those reasons, the fabrication of tubular burners is relatively expensive.
Flat burners are composed of two half shells and have the advantageous characteristic of having an integrated pilot burner, which is made of one piece therewith by bending the peripheral edges when the two half shells are joined. Therefore, any drawback associated to proper positioning is obviated. The main gas outlet holes and the holes for supplying gas to the pilot burner are obtained by perforation of one of the two half shells. In another type of flat burner, each half shell has a corrugated edge opposite to that of its respective opposite half shell and the gas/air mixture outlet holes are generated by coupling those edges. Although in this second case the perforation step is avoided, the holes still have a rather large size, which is further subjected to changes in the heating step, and sealing problems may also occur between the two half shells. Flat burners typically have advantages that cannot be found in tubular burners, which consist in that all connections, and particularly those for the flame safeguard and the igniter, are prearranged in an optimized manner, and there is no need to position them. Also, unlike tubular burners, flat burners may have inner walls for modulating gas distribution among the various holes, and the lack of these walls might cause unevenness problems, especially at low flame levels. Obviously, flat burners do not have the problem of the end-side closing member.
Despite of all these advantageous characteristics, flat burners provide no advantage in terms of modularity and size adaptability, particularly in length, with respect to different situations and/or oven sizes, whereby a dedicated burner must be manufactured for each cooker type, with a serious impact on costs.
Therefore, this invention has the object of obviating, by simple and inexpensive means, all the above drawbacks, and to provide a burner that has equal or better features than prior art burners. Particularly, a burner is desired that has all the advantages of a flat burner, particularly the integrated pilot burner and well secured igniter and flame safeguard, while maintaining all the construction adaptability and modularity characteristics of the tubular burner, particularly provided by the truncated end thereof, and that always ensures optimized operation in any circumstance, while limiting adaptation to the replacement of the nozzle and possibly to the adjustment of the gas/air stoichiometric ratio. Such a burner would allow the manufacturer to keep a limited number of parts in stock to manufacture burners.